The physiological role of luteinizing hormone-releasing hormone (LHRH) is being investigated using rats and hamster. Antibody to LHRH which has been generated in sheep is administered to animals to nullify the action of endogenous LHRH thereby revealing the physiological role of LHRH under various conditions, including estrous cycle, pregnancy and puberty. Radioimmunoassay of LHRH in the peripheral plasma is performed to observe the secretory patterns of this hypothalamic hormone in relation to the secretion of gonadotropins. Various synthetic antagonists to LHRH are also investigated to observe if they exert similar effects as the antibody to LHRH on the hypothalamo-pituitary gonadal functions, in hopes of using the synthetic antagonists for blocking ovulation, preventing nidation or terminating pregnancy. On the other hand, various synthetic agonists of LHRH are tested for their LH- and FSH- releasing activities in animals following the administration of these compounds through various routes to determine the most effective route and schedule of administration.